1. Field of the Invention
This invention relates to a method of producing char from concentrated waste liquor expelled from pulp manufacturing plants, which is applicable to all concentrated waste liquor materials generated by the plant.
2. Description of the Prior Art
The quality and properties of activated carbon are directly dependent on the properties of the material. Wood scrap such as saw dust; fruit shells, such as coconut shells; coals, such as bituminous coal, and the like are suitable starting materials for the preparation of activated carbon. However, waste liquor from the pulp manufacturing process is more attractive because such process ensures a large, steady, less expensive supply of starting material.
However, heretofore, no methods have been developed for the production of activated carbon from the waste liquor in the pulp manufacturing process. Only one company has collected unburned carbon from a plant which burns the waste liquor from the pulp manufacturing process and has adopted it as a source of carbon.
Previously, when char for producing activated carbon was produced from the waste liquor in pulp manufacturing, the waste liquor became highly viscous, and resulted in the generation of large lumps of material, so that uniform carbonization of the waste liquor was impossible. This difficulty arose because the lignin and saccharose components of the waste liquor undergo physical and chemical changes at high temperature. This has been a particular problem when rotary kilns have been used as a heat source, because the size of the lumps grows by granulating action as the kiln rotates so that the char cannot be uniformly carbonized. As a result, waste liquor concentrate adheres to the inner wall of carbonizing kilns, and eventually turns into ash. Furthermore, as the components of the waste liquor become molten, the fine pores of the char become closed, which disturbs the next step, that of activating the char, and therefore a high quality char cannot be obtained.
Prior art processes have caused air pollution, since fine dust is generated when the char is produced, and moreover, rotating the waste liquor from pulp manufacturing in kilns spatters and particulates the char which produces the fine dust which causes atmospheric pollution. Though the atmospheric pollution caused by the fine dust can be prevented by using a wet scrubber in the former case, pollution from waste liquor processing remains an unsolved problem.
A need exists, therefore, both from the standpoint of the health of the plant personnel and the elimination of the danger of explosion of the carbon dust to eliminate the fine dust.